Catalytic dehydrogenation



Nov. 20, 1945. CONN 2,389,342

CATALYTIC-DEHYDROGENATION Filed Aug. 10, 1942 CATALYST TOWERS 980 IO50Flo|5oo GAUGE PRESSURE MOTOR FUEL HOLVNOLLDVHJ HIGH OCTANE FRACTION TAR,ETC.

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F325;! zo 1 um: J QLL B 2 m INVENTOR 8 5 w. CONN Patented Nov. 20, 1945CATALYTIC D-E-HYDROGENATIO-N Miller Wade Conn, Bartlesville, kla.,assignor to Phillips Petroleum Company, a corporation of DelawareApplication August 10, 1942, Serial No. 454,311

1 Claim. (01. 196- 9) This invention relates to a process for preparingan improved high octane motor fuel or gasolinefrom any straight-runnaphtha or gasoline stock, especially'the normally liquid hydrocarboncondensate known as distillate and obtainedby known methods of recoveryfrom the hydrocarbon mixture naturally occurring in gas phase inso-called distillate wells'under very high pressures exceeding 1000pounds per square inch. As is well known, this condensate or distillatemaybe recovered from the well gas which is at a high pressure within theretrograde condensation range by lowering the pressure thereon andpreferably by simultaneously scrubbing or contacting with an absorbentliquid. Methods of recovery of the condensate will be found forexamplein Vaughan 2,133,774; Bays 2,135,319; Vaughan 2,151,248; Bays2,156,234; Walker et al. 2,174,336; Vaughan 2,198,098; B'ays 2,212,143;Roberts 2,213,996; Buckley 2,242,173}

Farris 2,245,028; Walker 2,272,503; Walker 2,278,750.

This distillate is normally liquid and may be approximately water-whitein color, or in some instances more orless colored, and may or maynothave been subjected to stabilization to remove the light end orwildness (C4 and lighter) so that the remainder willnot readilyevaporate. Broadly speaking the distillate liquid has many of theproperties of a medium to poor quality third-grade motor gasoline. It ispractically water-white, sweet, non-corrosive, low in'sulphur and gum,and susceptible to tetraethyl lead for raising the octane number.Practically all of it shows 10 to 20% boiling above 400 F. That is,80-90% of it is inthe gasoline boiling'range. Usually it has an initialboiling point in the neighborhood of 90 to 100 F. and is fairly welldistributed over the gasoline boiling range. A summary of typicalcharacteristics is given in the following tables:

2,262,744;. Bays TABLE A Summary of typical distillate characteristicsGravity, A P. I 54 to 70", average around 60 Reid vapor pressure TABLE BDistillation characteristics (A. S. 1'. M.)

I. B. P F 78-162 10% PL. 128-232 50% F 202-364 E. P. F 360-572 8 F255-462 Per cent over 400 F. B. P. per cent 0- 38 This distillate isproduced in large quantities on the Louisiana and Texas Gulf Coast, forexample, at Corpus Christi,'Texas.

It is a serious disadvantage of the condensate just described that itsoctane number-is extremely low so that if it is attempted to use it asor in motor fuel it necessary to add tetraethyl lead thereto insubstantial amounts in order to raise its octane number'to satisfactorylevels. Other disadvantages are encountered 'in the use of thedistillate as motor fueL-f 'Ihe distillate per se, of courseyis notsuitable for use as motor fuel, and furthermore fractionation to giveend-poin motor fuels results in pooryields of an inferior type fuel.

Other types of material known'as'straight-run naphtha or gasoline stockare subject to the same disadvantages as the condensate just described,and my invention-in its broader sense is applicable thereto. An'example-is straightrun gasoline made by the straight-run distillation ofcrude petroleum oil. Preferably the start- 2 ing material has been freedfrom butane and lighter hydrocarbons! It may contain substantialproportions of material higher boiling than. gasoline, such as kerosene,gas oil, and other components boiling up to 600 or 650 F. I may treateither'theentire distillate or naphtha or only that portion thereofwhich boils inthe gasoline range. 7

The principal object of the present invention is to provide a processfor improving the motor fuel characteristics of the straight-run naphthaor gasoline stock and especially the condensate or distillate of thetype described above. Another object is to manufacture an improved motorfuel of high octane rating from],the'c 0ndensate and thereby markedlyreduce the quantity of tetraethyl lead that mustlbe added: Numerousother objects of the present invention will more fully hereinafterappear- The accompanying drawing portrays agram; matically onearrangement of equipment that has been found very satisfactory forcarrying out the process of the present invention,

high octane materials will consist of the branched chain or isoparafiinsand certain highpctane aromatic constituents such as benzene, toluene,etc 'l r 1}.1 j

The residual material comprises the low octane components and, where theoriginal material was not within the gasoline range iasgwillgordinarilybe the case, also contains a large proportion boil; ing over and abovethe gasoline range@ This fraction is then, after; admixture with recyclegases and with recycle stock as hereinafter describedfpassed toaprehea'ter where it is brought to the catalytic conversion temperatureranging frorn '9'00 to 1100-F., and preferably from 980 to 1650 and theheated stream is passed through a body of catalyst capable of efiectinthe desired catalytic dehydrogenation and gas reversion of the-feed. Thepressure in'the conversionstep will .usually range from about 10 toabout 1500 pounds persquareinch gauge.

As catalystII usually-use granular bauxite, especially hard Arkansasbauxite, since it is comparatively inexpensive and easily obtainable andas effective a catalyst as any I have found. In-.

stead of 'bauxite, I may use chromium oxide, especially black unglowedchromium oxide, alumina, Activated Alumina, magnesia, catalysts of thetype known as,silica alumina.prepared by co-precipitating aluminumhydroxide and hydrous silica followed by calcining or by treating apartially dried hydrous silica gel with an aqueous [solution ofaluminum'salt such as aluminum chloride or sulfate followed by washingand drying or lprepared many other known manner, adsorbent Qclay such asfullers earth, acid-,

activated clay, charcoal, activated carbon, zirconium, oxide, eitheralone or in admixture with aluminum oxidebauxite impregnated withchromium oxidafbrucite, gypsum,.cadmium oxide, vanadium oxide,molybdenum oxide, tungsten oxide, zinc oxideycalic'he of the limestonetype, so-called Houdry catalyst, etc. Any of the synthetic catalystssuchas alumina or zirconia may be rendered in porus formas 'by theprocess'of Schulze 2,112,931. In the. case of chromium o'xide, it may bepresent in intimate admixture with a difiiculty reducible oxide ofaluminum, zir-' conium, titanium, silicon, thorium, boronor magnesium,as disclosed in Frey et a1. Reissue"21,911. It will alsobe understoodthat the metallic compound cataly ts may beisupporte'd on suitableine'rt or active carriers; Moreover the catalysts mentioned-are notnecessarily equivalents of one another.

"The reactions taking place in thecatalytic converter are notfully'understood. However it is established "that catalyticdehydrogenation and catalytic g'a's reversion '(polyform) ar'e'majorreactions "occurring. The dehydrogenation "effects conversion ofparaffins to olefins Some cyclization and aromatization mayalsoaccompany the dehydrogenation. Allo'f these reactions increase the antiknock 'r'ating of the hydrocarbon-mixture being treated. Thesesi'evers'ion' isa processin which occurs a reaction between normallyliquid hydrocarbons an normally gaseous hydrocarbons, and especially ofCa and C4 paraffins and olefins derived froin the catalytic efiiuent andthat are recycled to the converter, to form materials of good anti-knockproperties and in the gasoline boiling range. The catalytic as reversionwhich occurs simultaneously with the straight catalytic dehydrogenationinvolves reversion 'of-gaseous recycle with fresh feed, with unconvertedrecycle, and with polymerization products ordinarily formed in straightdehydrogenation. Due to the presence of substantial quantities oflighter material in the catalytic zon'e, increased yields are obtained.This gas reversion-is catalyzed by the catalyst employed.

In addition to the foregoing reactions, catalytic reforming also takesplace to a considerable excracking and formation of lower molecularweight materials with incomplete recombination also take place so thatnormally gaseous hydrocarbons available for recycling are continuouslyformed anew.

Other reactions may also takeplace in the conversion zone, such asisomerization, polymerization and depolymerizati'on, hydrogenation,catalytic alkylation, etc. Where sulfur is present,

40 catalytic desulfurization also occurs.

By reason of the presence of recycle hydrogen in the catalytic step,hydroforming may also take place.

Preferably the conditions are so adjusted that the extent of conversionper pass through the catalytic converter is at 1east20% and does notexceed 40% by weight based on the weight of fresh feed tothe converter.plus recycled normally liquid material.

If desired any normally gaseous material separated inthe firstfractionation Where unstabilized feed was employed, "and especially anyCa and C4 hydrocarbons such as propaneand butane, may be introduced asgas reactant to the catalytic conversion step.

The effuent from the catalytic conversion-zone is now fractionated intoat least four fractions and preferably five or even six fractions.

The overhead or first fraction is normally gaseous and containsthenon-condensible gases, n'am'ely Czhydrocarbons andlighter, i. e.,ethane, any ethylene, methane, and hydrogen. It may or may not containthecaand C4 hydrocarbons, 1. e., butane, any butenes, propane and anypropylene. This overhead fraction, whether or not it contains the Caan'd C4 components, maybe further fractionated to separateessentiallylpure hydrogenjwhich' is especially suitable for recycling.Where the C3 andC-i components are removed in this-overhead fraction,the fractionation may also separate a fraction consisting of'the C3 andC4 materials, these materials beingpar ticularly desirable as recyclestock, in addition tol the hydrogen. 1 i

A second fraction of intermediate "boiling" point and boiling in themotor fuel range is separated. This fraction constitutes the principalproduct of the process, it being of very good anti-knock quality, muchhigher than thefeed orthe gasoline portion of the feed. This fractionmay be used as such as motor fuel, with or without blending, butpreferably is blended with the high octane fraction initially separatedas described above, since these two fractions have difierentcharacteristics and compositions and mutually beneficialblendingproperties so that the resulting motor fuel is more rounded orbalanced, more complex and a better fuel. The product is a high octaneend poin motor: fuel and has improved lead susceptibility.

A third fraction consists of material heavier than the motor fuelfraction just described and comprises mainly unconverted material,incompletely converted material and other materials lighter than tarsand suitable for recycling. This third fraction is recycled in toto tothe catalytic conversion step for further conversion along with freshfeed from the first fractionation-step.

A fourth fraction comprising tars and the like heavy materialundesirable for recycling is separated in the fractionating step underdiscussion and discarded from the system.

As pointed out above, if'desired, the fractiona tion of theconversion-effluent may be so conducted as to separate afractionconsisting of the -C3 and C4 hydrocarbons which together with the purehydrogen or a suitable portion thereof or with a portion of the entireC2 and lighter fraction is passedpto the catalytic step' as the gasreactant for the gasreversion reaction therein. Usually an excess ofthis Ca and C4 fraction will be formed and it will be necessary to bleedoff a portion thereof continuously from the system.

As will be obvious, the fractionation of the catalytic eflluent may beconducted in one or a plurality of fractionators as necessary to givethe desired separation. .So-called superfractionation may be employed,if desired, for giving extreme closeness of cuts.

Referring now to the accompanying drawing, the raw distillate is fed vialine I into the first fractionator 2 (which may be one or severalcolumns) where a cut containing the high octane materials is separatedand passes out via line 3 whence it may be removed as such from the'system via line 4, though it is preferably blended with the mainproduct of the process to form motor fuel as will appear below.

The low octane and heavy cut formed in fractionator 2 passes via line 5,which traverses heat exchanger 6 where it is heated by the hot catalyticconverter efiluent flowing in line H], through heater I where it isbrought to conversion temperature preferably from about 980 to about1050 F., and thence via line 8 into one of catalyst towers 9 which arefilled with an appropriate solid catalyst.

The effluent from catalyst towers 9 passes via line I through heatexchanger 6 and thence into fractionator l I where it is fractionatedinto at least four cuts now to be described. A normally gaseous overhead(C4 and lighter) fraction is taken off via line 12 whence it may besplit, a portion passing via line I3 as recycle gases into the feed inline and the balance passing via line I4 to fuel or any other use. Afraction in the motor fuel boiling range (from about 100 F. to about 400F.), and which is the main product of my process, is taken off via linel5 and passed into admixture with the overhead cut from fractionator 2to form the preferred motor fuel prod'uctbf my invention.- :A thirdfraction higher boiling than the fraction leaving via line l5 andcomprising mainly unconverted or incompletely converted material isremoved via line l6 and recycled to line 5 for further treatmentincatalyst towers 9.

Occasionally it will be found desirable to effect a further separationin fractionator H (which may be either a single? column or a series ofcolumns as necessary" to'effect' the'desired fractionation) whereby theC3 and C4 are separated as a fractionby themselves, removed via line ITand a portion passedvia line l8 as the recycle gas into 1ine5', theexcess leaving via line l9. This C3 and C4 fraction will be composedmainly of propane. and butanes though propylene and butylenes may alsobe present in significant proportions. When this Ca and C4 fraction isused as the recycle gas for effecting the gas reversion in towers 9, no,or only asmall proportion of the non-condensible gases (C2 and lighterhydrocarbons. and hydrogen) removed via line I2 will be recycled vialine l3.

,Inany case, the excess gas leaving the system via line 14 may be passedto the flare, employed as fuel in the refinery, compressed and pumpedback into the formation whence the distillate was recovered, or put toany other desired use.

It'is desirable to always recycle a substantial amount of hydrogen inorder to protect the catalyst against premature carbonization anddeterioration, especially in the initial portion thereof. Thus, anespecially desirable way to operate is to recycle C3 and C4 materialvialine l8 and to treat the C2 and lighter non-condensible fractiontakenoif via line l2 (or a suitable portion of this fraction) in a unit2| to segregate substantially pure hydrogen from the hydrocarbon contentthereof, and recycle this essentially pure hydrogen in suitable amountto line. 5, the hy drocarbon gases so separatedleaving via line 22.However, hydrocarbons lighter than C3, such as ethane, ethylene andmethane, may also be recycled, inwhole or only in part, if desired.'Provision is made in fractionator II to withdraw as a bottom productvia line 20 any accumulation of unconverted products, tars and the likenot desirable to recycle to the system.

The advantages of the described mode of operation are many. Among themare: An overall inferior distillate or straight-run naphtha is initiallyseparated into its high and low octane fractions for separate treatment,thereby eliminating the necessity or disadvantage of cracking orprocessing branched chain high octain hydrocarbons by processingcatalytically only the low octane fraction. The process results in a94-98% yield of motor fuel hydrocarbons with a much improved octanenumber as compared with a previous yield of about of motor fuelhydrocarbons having an inferior octane number when using simplefractionation of the distillate to recover only the gasoline rangematerial. By recycling normally gaseous products derived from thefractionation of the catalytic effluent and also by recycling theheavier-than-motor fuel fraction similarly derived, under the conditionsof temperature and pressure shown, catalytic reforming is obtainedwhichmay involve hydrogenation, catalytic reversion, catalytic cracking,catalytic dehydrogenation, catalytic alkylation and catalyticdesulfurization or any possible hydrocarbon reactions to give betteryields 01' a superior qualit motor fuel. The process gives agself-contained, economically operated methodof converting fdis'tillateto a high grade the advantages of the invention. Ofthetotal 50 octane:raw condensate Y or distillate charged to asystem as described aboveapproximately 180% falls withinthe motor fuel range and has an cetanenumber of around58, which with 1 cc. of tetra ethyl ;1ead.gives 72octane motor lfuel. :By treatmentin accordance with the'foregoing so asto .obtain catalytic dehydrogenationand gas treversion of "the :low\octane out of this material, there .is obtained "an 85 to 90% yield ofmotor fuel which withl cc. of=tetraethyl leadgives anSOlQctanemateria-I. i

,The process :is applicable toany gasoline stock of the type known asfstraighterum that :is, to condensate or f distillate 'of the typedescribed at length above. Ordinarily "the stock "treated comprisesaPredominant proportion of material in the gasoline range,1that from'about 90 F. toabout 400 Fuor 425 F. Theastock may cover a range of froman initial ".point Lranging anywhere fromaabout 190 F. to about 200F. toan end point iranging anywhere "from -about .400 F. or 425 up to 2650 Fiand ordinarily -.is .fairly well distributed over sucha range.Ordinarily the stock treated bythe process of'my invention consistsessentiallyofparafl'ins most of which are unbranche'd and thereforevery'low'in octane'rating. However, small amounts ofunsaturates, i.e.,olefins, cyclo-o'lefins, 'etc., small amounts of arcmati'cs,cycloparaflin's, naphthenes,-etc., and substantial amounts ofisoparafilns of high octane rating maybe present.

As used herein, by the term high octane I mean having "an octane numberabove 60 and usually at least 70 and by low' octane I mean having anoctane number not over "60,Wlthllt using lead.

It "will be understood that the :foregoing disclosure is illustrativeonly 'andnot limitative, and

that the invention is to be taken as byzthe terms 'ofithe appendedclaim.

. A process which comprises subjecting a norw mally liquidcondensateobtained from the hydrocarbon :mixture occurring naturally in thegaseousphase in distillate 'wells under a pressure in excessof 1000pounds ,persquare inch to fracticnation to separate a first fractioncontaining the high octane'components in the motor fuel boiling rangeanda second fraction containing the low octane and heavier components,passing said second fraction in the presence of recycled hydrogen and C3and C4 hydrocarbons formedin this step in contact with'agranularbauxitecatalyst at a temperature within the range of approximately 900to approximately l100 Fhand ataipressurewithin the [range ofapproximately 10 tosapproximately 1500 pounds ;per square inch gauge,.fra'ctionating athe efiluent from the .lastnamed-step to recover atleast six fractions .as follows: a (1) 'a fraction consisting ofessentially pure hydrogen, (2) a fraction containing'C2 and lighter:hydrocarbons, ('3) a fraction containing Ca and cifhydrocarbons, (4) anormally liquid fraction'containing the high octane components -in themotor fuel boiling range, (5) a second liquid fraction containingithelow octane components and components heavier than those in the motorfuel boiling :range; includingunconverte'cl and (incompletelyconvertedrnormally .liquid components of the charge to said last -namedstep, and (6) a:fraction containing tars andheav-y material unsuitablefor recycling, recycling :at least a "portion of said hydrogen :fraction(fractional) :andat least ;a portion of said C3 and C4 fraction.(fraction'3) to said catalytic conversion step lrecyeling said secondliquid fraction (traction '5) to-said catalytic conversion step foradditional conversion along with fresh'material, and blending rsaidfirst-named .high octane fraction with :said second-named high octanefraction (fraction .4) .togive a high octane motor fuel.

MILLER WADE 'COlllV;

limited only;

